Substitution of plastic compositions for structural articles formed from non-plastic materials may meet objections regarding relatively low physical properties of the substitute plastic composition. Manufacturers often blend the plastic composition with other resins and additives to improve the physical properties. But, the blends of resins and additives may decrease the recyclability of the plastic composition.
In one example of a structural article suitable for material substitution, railroad ties support relatively great weights of railroad locomotives and their attached train cars with their contents. As the trains pass over railroad rails supported on railroad ties, the ties experience substantial vibration, in addition to the compressive force of the weight. When the ties are not in use, they are still subjected to harsh environment extremes of temperature, ultraviolet light, and moisture. The degradation of wooden railroad ties through this exposure to the environment requires that the ties must be replaced frequently in order to continue to perform their primary function of supporting the weight of the train. The wood used to make conventional railroad ties is increasingly becoming more expensive. Wooden railroad ties are heavy making the job of replacing them difficult.
Articles currently available and not an incorporating in-situ foam core have various deficiencies with regard to absorbing water, management of energy, lack of structure, excessive weight, or biological degradation
Manufacturers attempt to insulate an internal cavity of an article from the external environment. It is advantageous to have minimal thermal transfer between the internal cavity in the external environment. It is also advantageous to have the walls of the energy management system be as structural and as light as possible as well as economical. Adding more insulation increases the cost and weight of the energy management system article.
Certain manufacturers of energy management system articles use processes such as blow molding or vacuum forming followed by costly secondary operation of filling the cavity formed by the molding process with an injected foam, such as polyurethane foam. Other manufacturers of energy management system articles, such as refrigerators, have a large number of individual subcomponents, many of which involve bending of sheet metal, followed by secondary operations of filling the cavity formed by the subcomponents with injected foam.